Internal combustion engines used in automobiles typically operate on fuel-air mixtures, where a fuel injector supplies fuel and a throttle supplies air. On-board computers, programmed to be responsive to a signal from an accelerator in the automobile, determine the amounts of fuel and air. When a driver wishes to go faster, he or she depresses the accelerator, signaling the computer to supply more fuel and more air to the engine. The fuel injectors respond by supplying more fuel and the throttle responds by opening wider to admit more air to the cylinders of the engine. When the driver wishes to slow down, the driver lifts his or her foot from the accelerator, signaling the fuel injectors to supply less fuel and the throttle to move to a more closed position.
The throttle is typically an air valve, in which a butterfly valve on a shaft controls the flow of air. A gear train to a motor responsive to the on-board computer controls the shaft rotation, and thus the butterfly valve position. When the computer calls for more air, the shaft rotates in one direction to open the valve. When less air is needed, the shaft rotates in the opposite direction to close the valve. If the motor fails, the air valve or throttle must move to a safe condition. That is, the motorist wants any failure in the air valve train to be in fail xe2x80x9csafexe2x80x9d or closed condition, ceasing operation of the engine, rather than failing in an xe2x80x9copenxe2x80x9d position, which could lead to uncontrolled operation.
A spring wound onto the shaft during assembly of the throttle enables automatic closing of the throttle. When the shaft rotates to admit more air, it winds the spring and puts it into a state of torsion, in which the force or bias of the spring opposes the rotation of the shaft in that direction. If the motor fails, the spring biases the shaft in the opposite direction, closing the valve. During manufacture and assembly of the throttle, however, it is difficult to wind the spring, assemble it onto the shaft, and apply the proper amount of torsion for the desired operation. The present invention is directed to improvements in a torsion spring assembly, and particularly improvements to a torsion spring assembly used in an electronic throttle for automotive applications.
The present invention provides a unique insert used for winding the spring and assembling it onto a shaft of a throttle. One aspect of the invention is a torsion spring assembly. The torsion spring assembly may be used to move a throttle to a closed position. In one embodiment, the assembly preferably includes a helically wound spring having a plurality of coils, including a first coil and a last coil, the first and the last coils each having an end portion, or tang. The tangs may be bent at an angle to the body of the coils, such as a right angle, or they may extend radially or tangentially from the spring. One end of an insert is placed inside the spring to support and center the spring. This end of the insert has an aperture or hole for receiving one of the end portions of the spring, thus preventing the spring from free rotation. The other end of the insert has at least two slots and at least one tab.
In one embodiment, the torsion spring assembly includes a housing, the housing having slots to match the tabs of the insert when they are assembled together. The assembly also includes a load element, to be assembled concentric with the insert, with the load element having an aperture or hole for receiving the other end portion or tang of the spring. These parts are then preferably assembled with a winding tool. An assembler uses the winding tool to rotate the insert a specific angle so its tabs mate with slots in the housing. In one embodiment, the insert also centers the spring and prevents any unwanted motion. Winding the spring puts it into a state of torsion. After winding, the tabs of the insert mate with slots in the housing, and the torsion spring assembly includes the spring, the insert, and the load element on one side of the housing. A cap on the other side helps lock the insert into place and seals the spring from the external environment.
In other embodiments, other parts may be added in order to furnish a throttle assembly, including a motor and a gear train on the housing, and a gear or gear sector on the load element. A shaft with a valve, such as a butterfly valve, may be assembled concentric with the spring and the insert, the butterfly valve being part of a throttle with a throttle body. The motor is used to rotate the shaft, thus opening or closing the valve through the gear train. The throttle may also include a position sensor for feeding back position information to an on-board computer.
Another aspect of the invention is a method of moving a throttle to a closed position. In one embodiment, the method includes providing an electronic throttle, the throttle assembled with a return spring and an insert, the insert acting to center and support the spring, and when the throttle is assembled, the spring is put into torsion. The method preferably further includes opening the throttle and further torsioning the spring by opening the throttle, and the spring is held in torsion by the assembly. The method then includes closing the throttle by the torsion of the spring when a force holding the throttle open is released, and the spring causes the throttle to move in the opposite direction, closing the throttle.